The invention pertains to a lightweight structure, particularly a primary aircraft structure or a subassembly.
Aircraft fuselage cells in conventional aluminum construction are composed, for example, of four partial shells that are respectively joined into an approximately hollow-cylindrical fuselage section or a “fuselage barrel.” A plurality of consecutively arranged and interconnected fuselage sections is then assembled into the aircraft fuselage cell. In well-known monocoque construction, structural components such as, in particular, stringers, frames, angle brackets, skins, etc., of light alloys and/or of composite fiber materials are integrated into aircraft fuselage cells. Fuselage barrels may be alternatively manufactured of pre-impregnated, strip-shaped composite fiber materials (e.g., “prepreg” material, textiles, thermosetting polymers, thermoplastic polymers, etc.) by means of winding processes. It is furthermore known from the prior art to brace aircraft fuselage cells or similar lightweight structures of usually cylindrical or conical shape with a uniform grid of reinforcing elements (“Isogrid”).
In monocoque construction, stringers (longitudinal reinforcements) and angle brackets are placed on the partial shells and then riveted or welded thereto in order to reinforce the aircraft fuselage cell. Subsequently, frame segments are placed on the partial shell, aligned and riveted to the stringers and the skin by means of the angle brackets. The partial shells are then joined into a fuselage barrel by respectively arranging these partial shells such that they overlap one another by a few centimeters and a longitudinal seam (longitudinal joint) is created and then riveting the partial shells to one another. The thusly produced fuselage barrels are then pushed together, aligned relative to one another and respectively connected to one another by means of butt straps such that a transverse seam (butt joint) is formed. The stringers, as well as the frames, respectively are non-positively interconnected by means of couplings riveted thereon. At the end of the assembly process, brackets (“A, B and C brackets”) for the system installation in the structural assembly are positioned and mounted at the corresponding locations of the fuselage cell structure in dependence on the respective customer requirements.
However, the conventional methods for the construction of aircraft fuselage cells have a variety of inherent disadvantages. A statically unnecessary weight increase results from the overlapping design of the longitudinal and transverse seams. In addition, these methods complicate the utilization of novel production equipment that is able to assemble the stringers and frames in the form of an integral construction, i.e., particularly without couplings, in order to economically manufacture, for example, partial shells of great lengths. The latter-mentioned aspect is particularly important in view of the fact that composite fiber materials (e.g., CFRP) are increasingly utilized for structural components of aircraft fuselage cells. The use of the conventional riveting technology furthermore results in a weakening of the structure due to the required bores, in a weight increase due to the large number of required rivets, in sealing and corrosion problems, as well as in a higher manufacturing effort. In addition, the bracket installation in the fuselage cell is complicated, as well as time-consuming and cost-intensive with respect to the manufacturing technology, due to the broad variation of customer-specific adaptations.
Furthermore, particularly the stringers and the (annular) frames always respectively extend essentially parallel to the longitudinal aircraft axis and transverse thereto. In an aircraft fuselage cell realized in the form of a four-shell construction, however, the shells are subjected to very different mechanical load profiles in dependence on the operating state of the aircraft. For example, the lateral shells are usually subjected to high shear stresses while the top shell and the bottom shell are acted upon with compressive loads. However, a fuselage cell that is composed of a periodic grid-like sequence of stringers, frames and a skin cannot cope with the recorded differentiated load profile during the operation of an aircraft. This applies analogously to known reinforcing structures in other technological fields such as, for example, space travel, shipbuilding, automotive engineering and conventional or regenerative power engineering.
DE 10 2006 050 534 A1 discloses an integrated system of electrical and/or optical lines for an aircraft. On skin panels of fiber-reinforced plastic materials, the lines can be directly embedded into the fiber reinforcement and/or into the surrounding resin matrix. However, the aircraft fuselage cell is conventionally composed of skin panels, frames, stringers, angle brackets, etc., that represent a regular, repetitive three-dimensional structure.